1. Field of the Invention
This invention relates to a device for detecting the speed of transference of a moving body which is transferred or displaced linearly or in a rotational direction, which device can be effectively utilized, for example, as a rotational angle detecting sensor for detecting the rotational speed of a wheel or the like of a vehicle.
2. Description of the Related Art
Several devices for detecting a rotational speed of a moving body such as a wheel of an automobile are known; for example, a rotary encoder utilizing a magnet pick up system whereby the rotational speed is detected by providing a plurality of projected portions on an outer surface of a rotor made of a magnetic metal and a pair of a permanent magnet and a coil arranged to face the projected portions (Japanese Unexamined Patent Publication No. 59-31406), or such an encoder utilizing an optical system in which the rotational speed is detected by providing a plurality of slits thereon, instead of the above projected portions, and detecting and counting the permeation of light therethrough (Japanese Unexamined Patent Publication No. 61-167815).
However, in these known systems, a special shape such as a concave-convex configuration, or slits, must be formed on or in the outer surface of the rotor, and these known systems have a further drawback in that it is impossible to accurately calculate the rotational speed of a rotor because an angle of turn of the rotor during a predetermined time interval can not be determined when the rotor rotates at an extremely low rotational speed, since the angle of turn can not be determined from the positions defined by a space formed between adjacent projected or concaved portions or slits, and therefore, an increased ripple and a phase delay occur.